Regiospecific synthesis of 2,3-naphthylenebis(diphenylphosphines) by double insertion of alkynylphosphines into nickel(0)-benzyne complexes

Article abstract of DOI:10.1039/a802291g

The double insertion of diphenylprop-1-ynylphosphine into the nickel(0)-benzyne bond of the complexes [Ni(1,2-η-4,5-X₂C₆H₂)(PEt₃) ₂] (X = H, F) forms 2,3-naphthylenebis(diphenylphosphines) regiospecif

Full text of DOI:10.1039/a802291g

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Regiospecific synthesis of 2,3-naphthylenebis(diphenylphosphines) by double
insertion of alkynylphosphines into nickel(0)–benzyne complexes
Martin A. Bennett,*† Christopher J. Cobley, Eric Wenger and Anthony C. Willis
Research School of Chemistry, Australian National University, Canberra, ACT 0200, Australia
The double insertion of diphenylprop-1-ynylphosphine into
the nickel(0)–benzyne bond of the complexes [Ni(1,2-h-
4,5-X2C6H2)(PEt3)2] (X
=
H, F) forms 2,3-
naphthylenebis(diphenylphosphines) regiospecifically.
Small cycloalkynes or arynes, which are short-lived in the free
state, are stabilised by coordination to d10 transition metal
fragments such as ML2 (M = Ni, L2 = dcpe,‡ 2PEt3; M = Pt,
L2 = dcpe, 2PPh3).1 Unsymmetrical acetylenes (RC·CRA)
undergo double insertion into nickel(0)–benzyne complexes of
type 1 to give a mixture of isomeric naphthalenes (2a, 2b),
whose ratio is determined by the stereoelectronic properties of
the inserted alkyne (Scheme 1).2,3
Recently we have been interested in extending this chemistry
to alkynylphosphines, which could provide a novel route to
functionalised naphthylenebis(tertiary phosphines), potential
ligands that are not readily accessible by conventional synthe-
ses.4 Herein, we report the regiospecific reaction of diph-
enylprop-1-ynylphosphine5 with the Ni0–aryne complexes
[Ni(1,2-h-4,5-X2C6H2)(PEt3)2] (X = H 1a, F 1b) (Scheme
2).
Reduction of the appropriate (2-bromoaryl)nickel(ii) com-
plexes [NiBr(2-Br-4,5-X2C6H2)(PEt3)2] (X
lithium in diethyl ether at 240 °C, followed by evaporation of
= H, F) with
Fig. 1 ORTEP (25% probability) representation of 3b. Hydrogen atoms
have been omitted for clarity.
X
X
L
ether and extraction with hexane at 260 °C, yielded yellow
solutions of the complexes 1a and 1b that were used in situ for
all subsequent insertion reactions.2,3 The addition of 2.5 equiv.
of diphenylprop-1-ynylphosphine at 278 °C, followed by
warming to room temperature, resulted in a dark red solution
containing a complex mixture as shown by 31P{1H} NMR
spectroscopy. However, by addition of bromine, orange nick-
el(ii) complexes of type 3 were isolated and fully charac-
terised.§¶ The high overall yields of 3a and 3b (up to 97%),
together with the molecular structure determination of the
chelate, planar-coordinated dibromonickel(ii) complex
[NiBr2{C12H8F2(PPh2)}] 3b (Fig. 1), confirmed that the
reaction produced regiospecifically 2,3-naphthylenebis(di-
phenylphosphines) as the only observable insertion products.∑
Treatment of the initial dark red solutions with 1 equiv. of
Ni
L
R
R
RCCR'
X
–'NiL2'
R'
R'
X
X
R'
R
L = PEt3
X = H 1a, F 1b
+
X
R
R'
2a
Scheme 1
2b
Ph2
P
2.5 equiv.
Ph2PC2Me
X
X
X
X
L
PEt3
PEt3
Ni
Ni
L'
P
dcpe greatly simplified the
31P{1H}NMR spectra, which
Ph2
1a X = H
1b X = F
showed in each case the presence of a single Ni0 complex,
[Ni{C12H8X2(PPh2)2}dcpe)] (X = H 4a, F 4b), together with
free PEt3 and Ph2PC·CMe. On the basis of these results, the
31P{1H}NMR spectrum (202.4 MHz) of the dark red solution
could be assigned to a mixture of unsymmetrical nickel(0)–
tertiary phosphine complexes of type 5, all containing the newly
formed naphthylenebis(diphenylphosphine) with a combination
of PEt3 or Ph2PC·CMe as ancillary ligands (Scheme 2).
Reaction of 3a or 3b over 24 h at 50 °C with a large excess
of NaCN in Me2SO liberated quantitatively the pure 2,3-naph-
thylenebis(diphenylphosphines) 6a and 6b as white solids
{overall yields based on [Ni(cod)2] of up to 78%}.§¶
5a X = H
5b X = F
L = L' = PEt3 or Ph2PC≡CMe
L = PEt3 , L' = Ph2PC≡CMe
dcpe
–L, –L'
Br2
Cy2
P
Ph2
P
Ph2
X
X
X
X
P
Br
Br
Ni
Ni
P
Ph2
P
Cy2
P
Ph2
Exposure of 5a or 5b to air led to nickel–phosphine bond
cleavage and only partial oxidation of the naphthylenebis(di-
phenyl)phosphines, forming the mono(phosphine oxides)
C12H8X2(PPh2){P(O)Ph2 }7a and 7b,6 the structure of 7b being
3a X = H
3b X = F
4a X = H
4b X = F
Scheme 2
Chem. Commun., 1998
1307

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Notes and References
X
X
PPh2
PPh2
† E-mail: bennett@rsc.anu.edu.au
‡ dcpe = bis(dicyclohexylphosphino)ethane, Cy2PCH2CH2PCy2
§ Supplementary data describing full experimental details are available.
(See http://www.rsc.org/suppdata/cc/1998/1307)
¶ Selected NMR data for compounds 3, 4, 6–9: 3a: 31P{1H} NMR (CDCl3,
80.96 MHz) d 65.5 (s). 3b: 31P{1H} NMR (CDCl3, 80.96 MHz) d 65.8 (s);
19F NMR (CDCl3, 188.1 MHz) d 2132.6 [app. t, J(HF) 9.4 Hz]. 4a:
31P{1H} NMR (C6D6, 80.96 MHz) d 47.2 [t, 2J(PP) 26.6 Hz], 52.1 [t, 2J(PP)
26.6 Hz]; 4b: 31P{1H} NMR (C6D6, 80.96 MHz) d 47.4 [t, 2J(PP) 27.4 Hz],
6a X = H
6b X = F
confirmed by X-ray diffraction.∑ The stronger oxidising agent,
H2O2, was necessary to accomplish complete oxidation to the
bis(phosphine oxides), C12H8X2{P(O)Ph2}2 8a and 8b.
2
52.3 [t, J(PP) 27.4 Hz]; 19F NMR (C6D6, 188.1 MHz) d 2139.6 [app. t,
´
J(HF) 10.2 Hz]. 6a: 31P{1H} NMR (C6D6, 80.96 MHz) d 26.2 (s). 6b:
31P{1H} NMR (C6D6, 80.96 MHz) d 25.6 (s); 19F NMR (C6D6, 188.1
MHz) d 2138.5 [app. t, J(HF) 10.3 Hz]. 7a: 31P{1H} NMR [(CD3)2CO,
80.96 MHz] d 26.6 [d, 3J(PP) 37.4 Hz], 31.0 [t, 3J(PP) 37.4 Hz]. 7b:
31P{1H} NMR [(CD3)2CO, 80.96 MHz] d 26.3 [d, 3J(PP) 36.7 Hz], 31.0 [t,
3J(PP) 36.7 Hz]; 19F NMR [(CD3)2CO, 188.1 MHz] d 2135.3 (m), 2136.0
(m). 8a: 31P{1H} NMR [(CD3)2CO, 80.96 MHz] d 34.3 (br s); 8b: 31P{1H}
NMR [(CD3)2CO, 80.96 MHz] d 33.4 (br s); 19F NMR [(CD3)2CO] 188.1
MHz] d 2133.9 (br). 9a: 31P{1H} NMR (C6D6, 80.96 MHz) d 215.3 [dd,
3J(PP) 24.0, 3J(PP) 37.0 Hz], 67.7 [dd, 2J(PP) 46.4, 3J(PP) 24.0 Hz], 72.9
[dd, 2J(PP) 46.4, 3J(PP) 37.0 Hz].
Ph2
X
X
P
O
O
X
X
PPh2
P
Ph2
P
O
Ph2
7a X = H
7b X = F
8a X = H
8b X = F
∑ Crystal data and data collection parameters: 3b: C36H28Br2F2NiP2, M
= 779.07, red–brown rod, crystal size 0.42 3 0.14 3 0.12 mm, monoclinic,
space group P21/c (no. 14), a = 8.633(2), b = 22.707(3), c = 16.237(3) Å,
b = 97.49(2)°, U = 3155.8(9) Å3, Z = 4, Dc = 1.640 g cm23, m(Mo-
Ka) = 32.94 cm21, F(000) = 1560, analytical absorption correction; 7474
unique data (2qmax = 55.1°), 4594 with I > 2s(I); R = 0.046, wR = 0.036,
GOF = 1.40.
7b: C36H28F2OP2, M = 576.56, colourless plates, crystal size 0.44 3
0.19 3 0.06 mm, monoclinic, space group Cc (no. 9), a = 9.541(3), b
= 28.86(1), c = 11.187(4) Å, b = 106.87(3)°, U = 2948(2) Å3, Z = 4,
Dc = 1.229 g cm23, m(Mo-Ka) = 1.88 cm21, F(000) = 1200, analytical
absorption correction; 2667 unique data (2qmax = 50.1°), 1415 with I >
3s(I); R = 0.043, wR = 0.035, GOF = 1.33. CCDC 182/847.
Theoretical calculations7 suggest that the PPh2 moiety, like
CO2Me, is electron withdrawing. The regiospecificities des-
cribed above are indeed similar to those observed in the
insertion of methyl 2-butynoate, MeC·CCO2Me, into complex
1b, where the direction of insertion was believed to be
electronically controlled and to require p-coordination of the
alkyne.1–3 In agreement, preferential side bonding of the C·C
bond of Ph2PC·CMe to the Ni centre, as opposed to
coordination via the phosphorus lone pair, has been observed.
The reaction between equimolar quantities of [Ni(cod)2], dcpe
2
2
and Ph2PC·CMe gave the Ni0–h -alkyne species, [Ni(h -
Ph2PC·CMe)(dcpe)] 9a, as the main product; a small amount of
the P-bonded isomer 9b, was also formed (Scheme 3).
1 M. A. Bennett and E. Wenger, Chem. Ber./Recueil, 1997, 130, 1029 and
references therein.
2 M. A. Bennett and E. Wenger, Organometallics, 1995, 14, 1267.
3 M. A. Bennett and E. Wenger, Organometallics, 1996, 15, 5536.
4 A. J. Carty, N. J. Taylor and D. K. Johnson, J. Am. Chem. Soc., 1979, 101,
5422; D. K. Johnson, T. Rukachaisirikul, Y. Sun, N. J. Taylor, A. J. Canty
and A. J. Carty, Inorg. Chem., 1993, 32, 5544.
Cy2
P
Cy2
P
[Ni(cod)2]
+ dcpe
Ni
+
Ph2P Ni
+
Ph2PC≡CMe
P
Cy2
P
Cy2
5 A. J. Carty, N. K. Hota, T. W. Ng, H. A. Patel and T. J. OAConnor, Can.
J. Chem., 1971, 49, 2706.
Ph2P
9b
9a
6 A. Avey, D. M. Schut, T. J. R. Weakley, and D. R. Tyler, Inorg. Chem.,
1993, 32, 233; M. A. Bakar, A. Hills, D. L. Hughes and G. J. Leigh,
J. Chem. Soc., Dalton Trans., 1989, 1417.
7 E. Louattani, A. Lledo´s, J. Suades, A. Alvarez-Larena and J. F. Piniella,
Organometallics, 1995, 14, 1053.
Scheme 3
This chemistry is currently being investigated as a potential
method for the synthesis of water-soluble diphosphines. We
thank the Royal Society for the award of a Fellowship to
C. J. C.
Received in Cambridge, UK, 24th March 1998; 8/02291G
1308
Chem. Commun., 1998